1. Technical Field
The embodiments herein generally relate to receivers, and, more particularly to system and method to reduce channel acquisition and channel switch timings in demodulators and to reduce latency in overall demodulation cycle for multiple demodulation standards in communication receivers.
2. Description of the Related Art
Currently, television broadcasts all over world, include either digital and analog transmission which can be done via either of cable or terrestrial transmissions. A communication system is capable of tuning to both analog and digital signals received via either of terrestrial and cable transmissions. When a channel scan is run on a television, it has to scan channels from different transmissions (e.g., from digital terrestrial channel to analog cable channel and then to analog terrestrial channel to digital cable channel, etc.).
FIG. 1 is a typical block diagram of broadcasting one or more signals to a television system (e.g., a communication system). The block diagram includes an RF tuner 102, a demodulator 104, a media processor 106, and a display device 108. Channel scan cycle begins with the media processor 106 setting up the RF tuner 102 and the demodulator 104. If a Software Defined Radio (SDR) demodulator is used, demodulation standard is set up by downloading a standard specific code. The RF tuner 102 is tuned to a required frequency. In case of digital channels received either through cable or terrestrial transmissions, the demodulator 104 provides a Signal Lock (SL) status when a Transport Stream (TS) packet is received by the media processor 106. Upon receipt of the TS packet by the media processor 106, the TS packets are parsed, and channel information that corresponds to audio and video content is recorded. Thereafter, the media processor 106 builds a channel database based on the information recorded.
After the entire digital spectrum is scanned, the media processor 106 switches the demodulation standard on the demodulator 104 from digital to analog for both cable and terrestrial analog transmissions. The media processor 106 downloads a code relevant to analog channel scans. Thereafter, another scan for the entire analog transmission spectrum begins. In case of analog cable or terrestrial broadcasts, the RF tuner 102 provides a Signal Lock Status if the channel tuned to is active. The media processor 106 builds a channel database based on the information received.
With reference to FIG. 1, FIG. 2 is a table view illustrating a typical channel database built by the media processor 106 of FIG. 1 upon receiving information during digital and analog channel scans via both cable and terrestrial transmissions. The channel database includes a virtual channel field 202, a modulation type field 204, and a programs field 206. The channel database lists important channel parameters as information pertaining to a channel number, a modulation type for a channel, and a list of corresponding programs running on the channel.
Initial setup time is involved when a demodulation standard is setup on an SDR based demodulator. The setup time is essentially a time taken to download a relevant code. After the code is downloaded, the RF tuner 102 tunes into a specific frequency and outputs Intermediate Frequency (IF) data to the demodulator 104. Upon receiving the IF data, the demodulator 104 goes through an acquisition state followed by a tracking state. Thereafter, the demodulator 104 outputs (i) a TS packet for digital channels/standards and (ii) a Sound Intermediate Frequency (SIF) signal and/or a Composite Video Baseband Signal (CVBS) for analog channels/standards. The acquisition time for the demodulator 104 varies from one demodulation standard to another. During the acquisition state, a plurality of parameters are estimated which contribute towards time taken to perform a channel scan operation and also time taken during a channel change operation.
A channel change may include either a channel change within a single major channel in digital broadcasts (e.g., Channel 1, Programme 1 to Channel 1, Programme 2 of FIG. 2), or a channel change involves a change in frequency band from digital broadcast to digital broadcast with the same modulation type (e.g., a digital terrestrial to a digital terrestrial of FIG. 2). The channel change may also include a channel change involving change in frequency band but with a different modulation type (e.g., a digital terrestrial to a digital cable of FIG. 2).
When there is a channel change within the single major channel in digital broadcasts, the demodulator 104 is not required to perform any specific action. The media processor 106 handles a request for a channel change in such scenario. When there is a channel change within the same modulation type but involves a change in frequency band, the media processor 106 sets up the RF tuner 102 for the frequency change. The demodulator 104 loses synchronization since a new TS packet is received. The demodulator 104 then triggers the process of acquisition and tracking before outputting a Transport Stream (TS) to the media processor 106. The time taken to for this process increases the time of channel change.
When there is a channel change involving change in frequency band with a different modulation type, the media processor 106 sets up the RF tuner 102 for a frequency change. If the demodulator 104 is SDR based, a new code is downloaded. The demodulator 104 then triggers the process of acquisition and tracking before outputting (i) a TS packet to the media processor 106 for digital channels and (ii) CVBS output for analog channels. In such a scenario, the duration of code download further increases the time of channel change.
Currently, a channel scan operation and a channel change operation both have acquisition and tracking cycles which introduce latency in a demodulation cycle. During the channel change, the demodulator 104 has to go through the acquisition and tracking phases again which further add to the latency and channel change and scan timings. Accordingly, there remains a need for a demodulation system that reduces latencies introduced in one or more demodulation cycles each time a channel scan operation or a channel change operation is performed.